Method for the production of usable steam and non-toxic solids from geothermal brine

ABSTRACT

A method is provided for producing electric power from hot, pressurized geothermal brine containing dissolved toxic elements without significant precipitation of toxic solids. When sludge produced by the process is washed, non-toxic solids are produced which can be disposed of or utilized in an environmentally acceptable manner. The method includes removing geothermal brine from an underground aquifer, separating non-condensable gases therefrom, and handling the non-condensable gases separately from the processing of the non-condensable gas-free brine to prevent reactions therebetween. An air-free flashed brine handling system is established to prevent contact of air with the flashed brine, and all brine contacted with air is injected into the geothermal brine aquifer through a separate, corrosion-protected injection well. Steam derived from the brine is used to produce electric power, the steam being condensed in the process. The steam condensate is air-cooled, and is used in the steam condensation process. Air-contacted steam condensate is deaerated before being combined with the brine, some of the deaerated condensate being used for scrubbing the steam obtained from the brine. The isolation of non-aerated brine and deaerated condensate from aerated brine, the removal of non-condensable gases from the brine, and the washing of the sludge produced from the brine results in a non-toxic sludge in accordance with government-accepted standards.

This application is a continuation-in-part of application Ser. No.06/947,040, filed Dec. 29, 1986, now U.S. No. 4,763,479.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to the production of electricalpower using geothermal fluids and, more particularly, to a method forthe production of useable steam and non-toxic solids from geothermalbrine. The steam may be used for the production of electrical powerthrough steam turbines or the like, and the non-toxic solids aresuitable for beneficial use in an environmentally acceptable manner.

2. Background Discussion

Generally speaking, heat from the earth is an inexhaustable resource.The great majority of this heat is unavailable except in those instanceswhere the hot magma from the earth's interior has come into contact withwater, which often produces surface manifestations, such as hot springsand geysers. Geothermal brine, at temperatures of over 500° F., may bewithdrawn from large subterranean aquifers which are found in many areasof the world. Unfortunately, such brine is not inherentlypollution-free. In fact, the utilization of such brine for powergeneration may produce adverse environmental impacts in view of presentenvironmental standards.

Brine and steam from naturally occurring geyser activity has givenenjoyment to mankind since antiquity and, over the years, extractionwells drilled into the earth's surface to intercept the subterraneanaquifers have produced a steady, dependable supply of hot pressurizedbrine to the earth's surface. Brine removed from the aquifers is flashedinto useable steam leaving a spent brine having a super-saturated amountof solids therein, which subsequently precipitate to form a sludge.

Although the hereinabove-recited principal of extracting steam fromgeothermal brine is easily stated, its implementation is not withoutadverse environmental impact. In fact, the environmental considerationsfrequently prevent economical production of electrical power. Most ofthe environmental impact problems are associated with the composition ofthe geothermal brine. As hereinbefore noted, geothermal brines may havetemperatures over about 500° F., with pressures in the range of betweenabout 400 to about 500 psig. At these temperatures and pressures, thegeothermal brine easily leaches large quantities of salts, minerals andelements from the aquifer formation. As is well known, brinecompositions vary from aquifer to aquifer, but typically contain highlevels of dissolved silica, dissolved gases as well as dissolved toxicsolids comprising, for example, antimony, arsenic, copper, lead andzinc, the toxic solids being most objectionable from an environmentalimpact point of view. As may be expected, flashing of the geothermalbrine causes a super-saturated concentration of silica and dissolvedtoxic solids which can precipitate from the brine.

Without preventative measures, the impurities typically precipitate as atough scale throughout the process equipment, including the reinjectionwells for pumping the spent brine back into the aquifer forreplenishment. Experience has shown that in high pressure,brine-flashing vessels, heavy metal sulfide and silicate scaling is themost severe problem, while in the comparatively low temperatureatmospheric flashing portions of the system the scaling usuallycomprises silica and hydrated ferric oxide.

Disposal of spent brine is accomplished by injection, or pumping, of thespent brine down a nonproducing well into the aquifer. The motive forthis procedure is to prevent contaminants in the brine from entering theenvironment and to return unusable enthalpy and mass to the reservoir,thus reducing thermal pollution and perhaps prolonging the reservoirlifetime. Unfortunately, the precipitated contaminants in the spentbrine may eliminate or drastically reduce the permeability of theformation surrounding the injection well. Ultimately, this proceduremight destroy the overall permeability of the aquifer. Hence, suchprecipitated solids must be removed from the spent brine beforeinjection thereof in order to maintain the aquifer integrity and preventblocking of the injection well itself, which may cause costlyabandonment thereof or reconditioning in order to rejuvenate itsfunctionality.

A considerable amount of effort has been directed toward developingeffective processes for removing solids from the spent brine while atthe same time eliminating or at least very substantially reducing silicascaling in the flashed geothermal brine handling systems. For example,U.S. Pat. No. 4,439,535 to Featherstone, et al, discloses the inducedprecipitation of scale-forming materials, principally silica, from thebrine in the flashing stage by contacting the flashed brine with silicaor silica-rich seed crystals. This procedure induces silica,precipitating from solution, to deposit onto the seed crystals ratherthan on equipment surfaces. Because the seed crystals provide arelatively large surface area for receiving precipitated silica comparedto exposed surfaces of the flashing vessels and equipment, a majority ofthe precipitated silica is captured by the seed crystals and preventedfrom combining as a hard scale on interior equipment surfaces.

Unfortunately, seeding to capture precipitating silica as well as othersolids from the flashed brine results in an increased amount ofsuspended solids which cannot be effectively disposed of by injectionthereof. As hereinbefore noted, the suspended solids include heavy metalelements and compounds which may be toxic and must be treated ashazardous wastes if they are present in amounts greater than thatdefined by environmental standards.

In a typical geothermal brine power plant, suspended solids are settledfrom the spent brine in a clarifier. The clarifier separates orconcentrates the precipitated solids into a sludge and a clarified brineoverflow having a relatively small amount of suspended solids. Theclarifier also produces the seed material useable for capturingprecipitating solids as hereinbefore described. In this procedure aportion of the silica precipitate sludge is removed from the reactorclarifier and introduced into the flashed crystallization stage. Theremainder of the sludge, in a typical facility, is dewatered anddisposed as a solid waste.

The amount of waste can be considerable. For example, for a 10 megawattpower plant which requires a brine flow rate of about 1.2 million poundsper hour, more than 6 tons a day of sludge may be produced. Underheretofore known methods for operating a geothermal steam power plant,this sludge includes toxic elements and compounds which, as hereinbeforementioned, are considered hazardous unless they appear in amounts lowerthan the standards set by government authorities. As should beappreciated, the costs associated with disposal of toxic sludge can besubstantial and are expected to increase as toxic waste dumps becomemore scarce and/or remotely located.

The clarified brine is pumped into injection wells, but substantialamounts of clarified brine must be returned to the aquifer duringoperation of a geothermal power plant facility. For example, a 10megawatt geothermal brine power plant, as hereinbefore mentioned, has abrine flow rate of 1.2 million pounds per hour. Consequently, even smallamounts of fine suspended solids in the injected brine not removed bythe clarifier can cause the injection wells to plug and thereafterbecome inoperable or inefficient in disposing of the geothermal powerplant effluent. Significant costs are associated with reconditioning ofa plugged injection well. For example, as much as a million dollars maybe expended in order to recondition a well; hence, it is imperative toreduce the amount of suspended solids in the geothermal power planteffluent to as low a value as possible. When this is accomplished,however, more of these solids removed from the brine must be disposedof.

Typically, to separate fine particles from the spent brine, filters andponds are used in combination with the clarifier. After the bulk ofsolid particles is separated and removed as a sludge from the clarifier,the brine is filtered through a set of filters, interconnected in seriesand/or parallel, which are designed to remove suspended particles fromthe brine.

Ponding of brine is also a common method of concentrating solids. Inthis procedure the brine containing fins suspended solids is pumped intolarge outdoor vats or ponds, and allowed to stand for a time sufficientto allow the fine solids to settle to the bottom of the pond.Thereafter, the liquid is skimmed off and the accumulated sludge isdried and sent to toxic waste dumps along with dried sludge from thereactor-clarifier.

The present invention is directed to a method for the production ofuseable steam from geothermal brine while simultaneously producing aclarified liquid suitable for injection into the aquifer withoutsignificant plugging thereof, and solids having toxic elements belowthose limits defined as hazardous by government agencies such as theState of California. As can be appreciated from the hereinabovediscussion with regard to the costs associated with the disposal oftoxic wastes, the method of the present invention provide significanteconomic benefit. The economic feasibility of recovering useful steamfrom geothermal brine sources hinges upon operating the plant in anenvironmentally acceptable manner without the occurrence of costsassociated with the handling of toxic materials. These considerationsbecome more important each day as public awareness over the environmenthightens and stricter standards continue to be implemented by governmentagencies in order to regulate the production and disposal of wasteconsidered toxic.

Additional advantages and features of the invention will become apparentto those skilled in the art from the following description when taken inconjunction with the accompanying drawings.

SUMMARY OF THE INVENTION

A method of producing steam from geothermal brine comprising dissolvedtoxic elements without significant precipitation of toxic solids inaccordance with the present invention includes removing geothermal brinecomprising water, non-condensable gases, silica and toxic elements fromextraction wells drilled into an underground aquifer and removingnon-condensable gases from the geothermal brine to producenon-condensable gas-free brine. The non-condensable gases are handledseparate from processing of the non-condensable gas-free brine toprevent reaction therebetween with dissolved solids in thenon-condensable gas-free brine which can occur at temperatures andpressures less than the temperature and pressure of the geothermal brineas it is removed form the extraction well.

The non-condensable gas-free brine is flashed to produce steam andflashed brine and an air-free flashed brine handling system isestablished to prevent contact of air with the flashed brine. In thismanner, precipitation of solids with a high, concentration of toxicelements is eliminated or significantly reduced. The toxic elementsprevented from precipitation by the present process includes antimony,arsenic, copper, lead and zinc, among others. Also, in accordance withthe present invention, the method produces steam, non-toxic solids andspent brine suitable for aquifer injection. In this instance, theflashed brine is separated into a sludge and clarified brine, with theclarified brine being reinjected into the underground aquifer. Thesludge is washed to remove any dissolved toxic elements in order toproduce non-toxic solids.

In accordance with the present invention, the non-toxic solids maycomprise at most about 500 ppm antimony, about 500 ppm arsenic, about2500 ppm copper, about 1000 ppm lead and about 5000 ppm zinc. Theselimits are set by the State of California as the total threshold limitconcentration for toxic substances. More particularly, in one embodimentthe present invention produces non-toxic solids comprised, at most,about 240 ppm antimony, 123 ppm arsenic, about 1000 ppm copper, about1000 ppm lead and about 1000 ppm zinc.

When used in conjunction with a power plant, the method of the presentinvention is suitable for producing power without significantprecipitation of toxic solids. The non-condensable gas-free brine isflashed to produce steam and brine, and the steam is utilized to producepower and steam condensate. The steam condensate is injected into theunderground aquifer without co-mingling of the steam condensate withnon-condensable gas-free brine or the flashed brine to preventcontamination thereof. In this manner, unwanted precipitation of toxicsolids is eliminated or substantially reduced. An air-free flashed brinehandling system is established to prevent contact of air with theflashed brine, which can result in precipitation of solids having a highconcentration of toxic elements.

In order to produce both power and non-toxic solids, while minimizingthe number of wells needed to be corrosion-protected, the method, inaccordance with the present invention, includes separating the flashedbrine into a sludge and clarified brine, injecting the clarified brineinto the underground aquifer separately from the steam condensate, andwashing the sludge to produce a non-toxic solid. More particularly, themethod of the present invention includes establishing one or moreseparate injection wells having casings resistant to corrosion byconstituents in the steam condensate, and injecting the steam condensatethereinto. In this manner, one is able to produce non-toxic solids andlimit the number of injection wells which need to becorrosion-protected.

In a variation of the present invention, steam condensate from the powerplant is deaerated before being used in steam scrubbing portions of thepower plant and/or before being used for other purposes, such as pumpseal purging, in the brine production facility.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be more readily understood by reference tothe drawings in which:

FIGS. 1a and 1b diagram a hot geothermal brine power generating facilityoperated in accordance with the present invention; and

FIG. 2 is a diagram similar to FIG. 1a, and in which is shown relevantportions of a variation geothermal brine power generating facility whichenables steam condensate to be deaerated before being used for suchpurposes as steam scrubbing and pump seal purging.

Where the same parts and/or features are shown in more than one Figure,they are given the same reference numbers.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The process of the present invention for producing steam, power andnon-toxic solids can be better understood by the consideration of thegeothermal brine power plant facility 10, illustrated in FIGS. 1a and 1bin abbreviated block diagrams.

Extraction wells 12 are utilized to remove geothermal brine from anunderground aquifer 14. It is to be appreciated that while only twowells 12 have been illustrated in FIG. 1a, a larger number of wells maybe used to provide the total input brine requirements of the facility10. The electrical power generating capability of the facility 10 mayvary according to the size of the facility; however, in connection withthe description herein provided, the parameters of the facility and theflow rates recited refer to a facility having a 10 megawatt poweroutput. For this power output, the facility 10 requires a total brineflow of about 1.2 million pounds per hour of geothermal brine at a wellhead temperature of about 500° F. and a pressure of about 450 p.s.i.g.

Extracted brine from the wells 12 typically contains non-condensablegases, silica and toxic elements. To remove the non-condensable gas, theextracted brine is fed through conduits 20 and 22 to a separation stage24 including wellhead separation vessels 28 and 30. The removednon-condensable gases are handled separately from non-condensablegas-free brine delivered to a flash/crystallization stage 34 viaconduits 36, 38 to prevent reaction therebetween with dissolved solidsin the non-condensable gas-free brine which can occur at temperaturesand pressures less than the temperatures and pressures of the brine asit is removed from the aquifer 14 by the extraction wells 12.

In the wellhead separators some steam escapes with the non-condensablegas. Non-condensable gases and steam delivered to a steam conditioningstage 40 via conduits 42, 44, 46 enters a steam wash scrubber 50.

In addition to the steam wash scrubber 50, the steam conditioning stage40 includes a final steam wash scrubber 52 interconnected therewith viaconduit 54. Steam passes through the steam wash scrubber 50 and finalsteam wash scrubber 52 through an exit conduit 58 to a conventionalpower generating facility 62 for subsequent generation of electricalpower. Water from the scrubbers 50, 52 exits via conduits 64, 66 andthereafter passes through a discharge conduit 68 to a diffuser sumpsettling tank 80 (FIG. 1b). Since this water has been contacted withair, the present invention provides for its separate handling andimportantly separate injection into the aquifer 14, as hereinafterdescribed.

The power generating facility 62 produces about 200,000 pounds ofcondensate per hour, which corresponds to the extraction rate in excessof about 1.0 million pounds per hour of brine from the extraction wells12. While lower and higher brine flow rates may be handled, the presentinvention has best advantage at higher brine flow rates for commercialutilization of the brine. Discharge of the condensate is through aconduit 88 to a condensate holding stage 90 and thereafter into theaquifer 14 via a separate injection well with other aerated brine aswill be hereinafter described.

Continuing with a description of the facility 10, the flashcrystallization stage 34 includes a high pressure flash crystallizer 94,a low pressure crystallizer 96, and an atmospheric flash tank 98. Brineis introduced into the high pressure flash crystallizer 94 from thewellhead separators 28, 30 via conduit 36, 38 and the conduit 100 whereit is subjected to an operating pressure of about 100 p.s.i.g. At thisreduced pressure, the brine instantly flashes, or boils, releasinguseful steam and producing brine supersaturated with dissolved solidsincluding silica. Before leaving the high pressure crystallizer, thesteam generated therein is subjected to a steam washing system 102 toreduce the amount of impurities therein and thereafter fed through asteam conduit 104 for introduction into the steam conditioning stage 40via conduit 46.

Flashed brine from the high pressure flash crystallizer 94 (FIG. 1a) isfed through a conduit 108, to the low pressure flash crystallizer 96which is usually operated at a pressure between atmospheric and about 50p.s.i.g. At this point, additional steam is flashed from the brine, andsuch steam is fed through conduits 110, 112 to the atmospheric flashtank 98 at which point it is discharged into the atmosphere.Alternatively, the steam released in the low pressure flash crystallizer96 may be used for heating or other energy-related purposes within thegeothermal power facility 10 and for blanketing clarifiers 118, 120 in aprimary clarification stage 122 and secondary clarification stage 124,respectively, steam being provided thereto by conduits 128, 130,respectively. Flashed brine from the low pressure crystallizer 96 is fedvia a conduit 134 into the atmospheric flash tank 98. Brine, includingsuspended solids with silica precipitate therein from the atmosphericflash tank 98, is transported through a conduit 136 to the separationstage 122 which includes the clarifier 118, a filter press 140 and awater wash 142.

A portion of sludge from the clarifier 118, is fed via a conduit 146 andpump 148 back into the high pressure flash crystallizer 94 to act asseed material. The remainder of the sludge is sent to the filter press140 by a conduit 150 to remove excess liquids. Thereafter, the solidsare washed to remove any remaining dissolved toxic solids to produce anon-toxic solids suitable for use as a building material, when combinedwith cement, soil conditioner or other uses. In accordance with thepresent invention, wash water containing dissolved toxic solids is sentto a settling pond and thereafter separately disposed of with otheroxygen containing brine as will be hereinafter described. Brine from thefilter press is conveyed via a conduit 152 to be combined with steamcondensate and separately injected into the aquifer 14 as hereinafterdescribed.

Clarified geothermal brine is discharged from the clarifier 118 througha brine conduit 154, pump 156 and conduit 158 into the secondaryclarifier 120 in the secondary clarification stage 124. (FIG. 1b).

Generally comprising the secondary brine clarification stage 124 is theclosed, secondary clarification vessel 120, a flocculating agent tank160, a relatively small, high flow rate emergency filter 162 and afilter backwash brine holding tank 164 as well as pumps 168, 170, 172,174 and 176. The secondary clarifier vessel 120 may be of ametallurgical reactor type which is formed having a large internalreaction well 180 with rotatably driven mixing blades 182 mounted on avertical shaft 184 therein. Rotatably driven scraper blades 186 areprovided below a partially open bottom 188 of reaction well 180.

Clarified brine overflow from the clarifier 118 is flowed, throughconduit 154, and pump 156, conduit 158, into upper regions 196 of thesecondary clarifier reaction well 180. Steam may be flowed from lowpressure flash crystallizer 96, through conduits 110, 130 into the topof secondary clarifier vessel 120 to provide a steam blanket 200 over abrine surface 202 in the vessel 120 and to exclude air from the vessel,as it is considered important to avoid increased brine acidificationcaused by air oxidation of ferrous ions naturally present in the brineto ferric ions, as well as reduce the production of toxic elements.Alternatively, inert gas may be used to blanket the brine in both theclarifier 118, 120 as indicated by arrow 206 in FIG. 1a.

A flocculating agent may be fed by pump 168 through conduits 208 and 210from flocculating agent tank 160 into brine effluent conduit 158. Withinconduit 158, the flocculating agent is inter-mixed with the clarifiedbrine before the brine is discharged into secondary clarifier vessel120.

Within secondary clarifier vessel 120, the inflowing brine is naturallycirculated down and around reaction well 180 (direction of Arrows A&B,FIG. 2a), while at the same time mixing blades 182 are rotated so as toprovide good brine-flocculating agent contact within the reaction well.

The secondary clarified brine overflow from vessel 120 is dischargedthrough an overflow conduit 216 to injection pump 218. Preferably, thesolids content of the secondary clarified brine overflow is less thanabout 20 parts per million, with means particle size being between about3 and about 4 microns. Within vessel 120, the settling solids are rakedby means 186 to a solids-brine discharge conduit 220 located at thebottom 222 of the vessel.

A portion of the solids-brine underflow from secondary clarifier vessel120 is recirculated to the inlet 224 of the vessel at a rate maintainingthe solids concentration in reaction well 180 within a particular weightpercent range. This particular weight percent range is preferablybetween about 0.5 and about 3 weight percent, with the more preferredweight percent being about 1.5 percent.

Pump 172 is connected to discharge conduit 220 for pumping some of thesolids-brine slurry or sludge from vessel 120, through a conduit 228, tobrine inlet 224. The rest of the slurry from vessel 322 is pumped bypump 172, through conduits, 230, 232, to the filter press 140. Valves234 and 236 in respective conduits control the division of sludge pumpedby pump 172 between brine inlet 224 of the clarifier 120 and filterpress 140.

Should the concentration of residual solids suspended in the brineoverflow from secondary clarifier vessel 120 unexpectedly exceed safe orallowable reinjection limits, the brine overflow from the vessel may betemporarily diverted, through a conduit 240, to pump 174 which thenpumps the brine through a conduit 242 into emergency filter 162. Afterpassing through filter 162, the brine is flowed through a conduit 244back into conduit 216 leading to injection pump 218. Valves 248, 250 and252 enable the brine overflow from secondary clarifier vessel 120 to bediverted around (as is the usual case), or alternatively to be flowedthrough, emergency filter 162. It is to be appreciated that brineoverflow from secondary clarifier vessel 120 is flowed through filter162 only until normal secondary clarification of the brine isreestablished in vessel 120.

Associated with filter 162 is a backwash holding tank 164, whichreceives brine overflow from vessel 120 through a conduit 254 connectedto brine conduit 216. Valve 258 in conduit 216 downstream of conduit 254and a valve 260 in conduit 254 enable the diverting of brine frominjection pump 218 into holding tank 164. To enable filter backwashingbackwash pump 176 pumps brine from holding tank 164 through conduits 264and 266, as well as through control valve 270 to filter outlet conduit244 upstream of valve 252.

The process of the present invention utilizes a unique injection stage276 for returning fluids to the aquifer 14 and includes a plurality ofconventional injection wells 278 and at least one spaced apartdesignated injection well 280 for the acceptance of aerated brine, thatis, oxygen containing aqueous liquids produced by the process such asthe steam condensate, water from the steam wash scrubber, filter pressbrine, dirty wash water all of which contain dissolved, corrosiveconstituents and/or toxic elements. While otherwise conventional innature, the designated injection well 280 preferably includes corrosionresistant casings, selected with the consideration that the brineinjected thereinto is cooler than that injected into the conventionalinjection wells 278, while at the same time having a relatively highoxygen content.

Because a separate injection well 280 is used to receive aerated brine,the majority of injection wells 278 handling non-aerated brine do nothave to be provided with corrosion resistant casings. This hassignificant economic advantage since it is expected that the designatedinjection well 280 will take less than ten percent, usually less thanfive percent and preferably less than about three percent, of the totalbrine injected into the aquifer 14. In addition, separated injection ofaerated and non-aerated brine prevents plugging of the injection welldue to precipitation of solids which occurs as a result of mixing of theaerated, non-aerated brines.

The handling of the aerated brine separate from the flash crystallizerstage 34 which produces useable steam for the power generating facility62 is of utmost importance. Heretofore, steam condensate from the powergenerating facility 62 has been processed to remove solids therein andreturned to the general brine handling system via the low pressurecrystallizer or the atmospheric flash tank in order to conserveenthalpy. However, it has been found that comingling of brine which hasbeen exposed to oxygen, or aerated, causes undesirable precipitation ofdissolved toxic solids. Hence, in accordance with the present invention,the steam condensate is disposed of by storing it in a conditioning, orsettling, tank 90, and thereafter separately injected with otheroxygen-containing streams into the designated injection well viaconduits 288, 290 and pump 292.

As hereinabove mentioned, the aerated brine produced in the process suchas water from the steam scrubbers 50, 52, dirty wash water from thewater wash stage 142, and emergency steam release, if any, from reliefvalves (not shown) within the facility are delivered to adiffuser-settler 80 by conduits 68, 156, 296, respectively, andthereafter combined with other oxygen-containing streams and injectedinto the designated injection well by a conduit 300, pump 292 andconduit 290. Additionally, steam which may be diverted from the steamblanketing line 130 may be diverted by a conduit 302 into thediffuser-settling tank wherein it is cooled, condensed and thereafterinjected into the designated injection well.

Brine from filter press 140 is combined with steam condensate in thebrine/conditioning storage tanks via line 152 and subsequently disposedof into the designated injection well 280.

The present invention may be further described with reference to thefollowing example:

EXAMPLE

When the facility 10 hereinabove described is operated at steady stateconditions, a sample of solids is taken from conduit 306 exiting thefilter press 140 and another sample is taken from the washed solidsremoved from outlet 304 from the water wash 142. These samples aredried, and the moisture and water-soluble and water-insoluble contentsof the settled sludge are calculated from the weight losses of the twosamples. The dry, washed sludge is given a Waste Extraction Test (WET)in accordance with the California Assessment Manual (CAM) a fulldescription of the test being set forth therein. The WET results of thewashed sludge are shown in Table 1. As can be seen, all of the toxicelements are below the Soluble Threshold Limit Concentrations (STLC)requirements of the CAM.

The characterization results of the washed sludge and the comparison ofits analysis with the Total Thresholds Limit Concentrations (TTLC)stated in the CAM are shown in Table 2. It is found that under theprocedures set forth in the present invention that the concentration oftoxic elements are below the Total Threshold Limit Concentrations setforth in the CAM. Removing non-condensable gases by wellhead separators230, keeping aerated and non-aerated brine streams separate from oneanother within the facility,

                  TABLE 1                                                         ______________________________________                                        RESULTS OF WASTE EXTRACTION TEST ON SLUDGE                                                SOLUTION ANALYSIS                                                                              STLC                                             ELEMENT     (mg/l)           (mg/l)                                           ______________________________________                                        As          1.1              5                                                Ba          23.0             100                                              Be          0.1              0.75                                             Cd          <0.1             1                                                Co          <0.2             80                                               Cr          <0.1             5                                                Cu          0.2              25                                               F           10.2             180                                              Hg          0.005            0.2                                              Mo          <0.3             350                                              Ni          <0.2             20                                               Pb          2.2              5                                                Sb          <0.5             15                                               Se          <0.01            1                                                Tl          <0.4             7                                                Ag          <0.1             5                                                V           <0.1             24                                               Zn          2.2              250                                              ______________________________________                                    

                  TABLE 2                                                         ______________________________________                                        ANALYSIS OF SLUDGE                                                            ______________________________________                                        SETTLED SLUDGE:      Moisture     18%                                                              Water soluble                                                                              11%                                                              Water insoluble                                                                            71%                                         WATER INSOLUBLE:     Average particle size                                                   (Coulter)  14 um                                               X-RAY DIFFRACTlON:   MAJOR: Barite with minor                                                      cation substitution                                                           TRACE: Fluorite                                          ______________________________________                                        ELEMENT    ANALYSIS (ppm)  TTLC(ppm)                                          ______________________________________                                        Sb         240             500                                                As         123             500                                                Ba         109,000         10,000*                                            Be         36              75                                                 Cd         <10             100                                                Cr         <9              500                                                Ca         <20             8,000                                              Cu         <1,000          2,500                                              F          13,000          18,000                                             Hg         <0.1            20                                                 Mo         <30             3,500                                              Ni         <20             2,000                                              Pb         <1,000          1,000                                              Ag         117             500                                                V          <9              2,400                                              Zn         <1,000          5,000                                              Al         <1,000                                                             Fe         62,000                                                             Si         259,000                                                            Mn         2,880                                                              Co         18,300                                                             Sr         6,800                                                              CO3        <150                                                               Cl         2,510                                                              Total Solids                                                                             34,000                                                             ______________________________________                                         *Excluding Barite                                                        

blanketing the brine in the clarifier and secondary clarification stage124 with steam or inert gas, and washing the solids to remove dissolvedtoxic elements has been found to produce a sludge having lowconcentrations of toxic elements. It has also been found that when theuse of wellhead separators to remove non-condensable gases isdiscontinued, copper concentrations in the washed solids exceed the CAMstandards set forth in Table 2. In explanation of this, it is theorizedthat the non-condensable gases, if not removed by the separators, reactwith the dissolved solids in the brine at lower temperatures andpressures and that this reaction occurs in the high pressurecrystallizer, resulting in precipitation of a copper compound. Thewellhead separator reduces the time and increases the pressure andtemperature during which the gas-brine can react. As shown in Table 2,when non-condensable gasses are removed, the copper concentrations arebelow the CAM limits.

VARIATION OF FIG. 2

As above-described in relation to FIGS. 1a and 1b, specialcorrosion-protected injection well 280 is provided for the injection ofaerated brine. Also injected into such injection well 280 is steamcondensate which is discharged from power generating facility 62,through conduit 88, into condensate holding stage 90. This manner ofdisposing of steam the condensate from power generating facility 62 ispreferred because the hot condensate is generally saturated with oxygenas a result of having flowed through an open cooling tower (not shown)in the power generating process and is, therefore, relatively corrosive.

It has, however, been found advantageous, in some circumstances, to usethe steam condensate from power generating facility 62 for variouspurposes, instead of disposing of the condensate in aerated brineinjection well 280. Therefore, in a variation geothermal brine powerplant facility 10a depicted in FIG. 2, some (or all) of the steamcondensate discharged from power generating facility 62 through conduit88 is diverted from from such conduit, through a conduit 398, into acondensate deaerator 400 in which oxygen is stripped from the condensatein a manner known to those skilled in the art.

By way of example, with no limitation intended or implied, deaerator 400may comprise a "Uni-mod" atomizing deaerator manufactured by CRANECochrane Environmental Systems, which is located in King of Prussia, Pa.Within such a deaerator 400, the condensate from conduit 398 is heatedto its boiling point by steam supplied to the deaerator, through aconduit 401, from low pressure flash crystallizer 96. Preferably, foruse with a typical 10 megawatt geothermal brine power plant facility10a, deaerator 400 has a condensate deaerating capacity of about 100gallons per minute and is capable of reducing the oxygen content of thecondensate from a typical level of about 1 PPMW (part per million byweight) down to a preferred level of no more than about 50 PPBW (partsper billion by weight), and to a more preferred level of no more thanabout 10 to about 20 PPBW. Although perhaps unnecessary, it is possiblethat deaerator 400 can reduce the oxygen content of the treatedcondensate to below about 2 PPBW.

Deaerated condensate is discharged from deaerator 400, through a conduit404, to a condensate pump 406, which pumps the condensate, throughconduits 408, 410, and 412, into steam scrubbers 50 and 52. Surplusdeaerated brine may be pumped (by pump 406) into atmospheric flashvessel 98, through a conduit 414 connected to conduit 408.

In addition or alternatively to pump 406 pumping deaerated condensate tosteam scrubbers 50 and 52, deaerated condensate may be pumped, through aconduit 416, for such other uses as pump seal purging wherein the use ofdeaerated condensate is preferred over non-deaerated condensate becauseof reduced corrosion problems.

Various valves (not shown) are provided in association with deaerator400 for purposes of controlling the flow of condensate into thedeaerator and for controlling the distribution of deaerated condensatefrom the deaerator.

Other than as described above, power plant facility 10a is preferablyidentical to the above-described power plant facility 10 (FIGS. 1a and1b).

Although a particular embodiment of the invention and a variationthereof have been described for the purpose of illustrating the mannerin which the invention may be used to advantage, it will, of course, beunderstood that the invention is not limited thereto, since manymodifications and variations can be made, and it is intended to includewithin this invention any and all such modifications and variations asfall within the scope and spirit of the appended claims.

What is claimed is:
 1. A method of producing steam from geothermal brinecomprising dissolved toxic elements without the significantprecipitation of toxic solids, said method comprising:(a) removinggeothermal brine comprising water, non-condensable gases and toxicelements from an extraction well drilled into an underground aquifer;(b) removing non-condensable gases from the geothermal brine to producenon-condensable gas-free brine and maintaining the non-condensable gasesseparate from the non-condensable gas-free brine to prevent reactiontherebetween the dissolved solids in the non-condensable gas-free brine;(c) flashing the non-condensable gas-free brine to produce steam andflashed brine; (d) introducing the flashed brine into an air-freehandling system to prevent contact of air with the flashed brine; (e)condensing at least some of said steam into steam condensate; (f)contacting at least some of the steam condensate with air; (g)deaerating at least some of the condensate which has been contacted withair; and (h) combining at least some of the deaerated condensate withsaid flashed brine.
 2. The method as claimed in claim 1, wherein thecondensate is deaerated so that the oxygen content in the condensate isno more than about 50 PPBW.
 3. The method as claimed in claim 1,including the step of using deaerated condensate for scrubbing the steamproduced from the geothermal brine.
 4. A method of operating ageothermal brine power plant for producing power without significantprecipitation of toxic solids, said method comprising:(a) removinggeothermal brine comprising water, non-condensable gases and toxicelements from extraction wells drilled into an underground aquifer; (b)removing non-condensable gases from the geothermal brine to producenon-condensable gas-free brine and maintaining the non-condensable gasesseparate from the non-condensable gas-free brine to prevent reactiontherebetween the dissolved solids in the non-condensable gas-free brine;(c) flashing the non-condensable gas-free brine to produce steam andflashed brine; (d) generating power with the steam and producing steamcondensate; (e) contacting at least some of the steam condensate withair; and (f) deaerating at least some of the steam condensate which hasbeen contacted with air; (g) combining at least some of the deaeratedcondensate with the non-condensable gas-free brine or the flashed brine;and (h) introducing the flashed brine into an air-free handling systemto prevent contact of air with the flashed brine.
 5. The method asclaimed in claim 4, including the step of injecting brine or condensatewhich contains significant amounts of air into the ground through acorrosion-protected injection well.
 6. The method as claimed in claim 4,including the step of using deaerated condensate from step (f) forscrubbing steam produced from the geothermal brine.
 7. The method asclaimed in claim 4, including the step of using deaerated condensatefrom step (f) for the purging of seals of pumps used for pumping thegeothermal brine.
 8. the method as claimed in claim 4, wherein thecondensate to deaerated so that the condensate has an oxygenconcentration of no more than about 20 PPBW.
 9. A method of operating ageothermal brine power plant for producing electric power, said methodcomprising:(a) removing high temperature and high pressure geothermalbrine from one or more extraction wells drilled into an undergroundgeothermal brine aquifer; (b) flashing the brine to a reduced pressureto produce steam and flashed brine; (c) generating power with the steamand producing steam condensate; (d) contacting at least some of thesteam condensate with air; (e) deaerating at least some of thecondensate which has been contacted with air; (f) combining at leastsome of the deaerated condensate with either the brine or the flashedbrine; (g) separating flashed brine which has become contaminated withair from flashed brine which has not been contaminated with air; (h)injecting the flashed brine which has not become contaminated with airinto the ground through one or more injection wells; and (i) injectingthe flashed brine which has been contaminated with air into the groundthrough one or more corrosion-protected injection wells.
 10. The methodas claimed in claim 9, including the step of using at least some of thedeaerated condensate from step (e) for scrubbing steam produced from thegeothermal brine.
 11. The method as claimed in claim 9, wherein thecondensate is deaerated in step (e) so that the oxygen content in thecondensate is no more than about 50 PPBW.
 12. A method of operating ageothermal brine power plant for producing electric power, said methodcomprising:(a) removing high temperature and high pressure geothermalbrine from one or more extraction wells drilled into an undergroundgeothermal brine aquifer; (b) flashing the brine to a reduced pressureto produce steam and flashed brine; (c) generating power with the steamand producing steam condensate; (d) contacting at least some of thesteam condensate with air; (e) deaerating at least some of the steamcondensate which has been contacted with air so that the concentrationof oxygen therein is no greater than about 50 PPBW; and (f) using atleast some of the deaerated condensate for scrubbing the steam producedfrom the geothermal brine.
 13. The method as claimed in claim 12,including the additional steps of:(aa) separating flashed brine whichhas become contaminated with air from flashed brine which has not beencontaminated with air; (bb) injecting the flashed brine which has notbecome contaminated with air into the ground through one or moreinjection wells; and (cc) injecting the flashed brine which has beencontaminated with air into the ground through one or morecorrosion-protected injection wells.
 14. The method as claimed in claim13, including the step of using at least some of the deaeratedcondensate from step (e) for purging the seals of pumps used to pump thegeothermal brine.
 15. A method of operating a geothermal brine powerplant for producing electric power, said method comprising:(a) removinghigh temperature and high pressure geothermal brine from one or moreextraction wells drilled into an underground geothermal brine aquifer;(b) flashing the brine to a reduced pressure to produce steam andflashed brine; (c) generating power with the steam and producing steamcondensate; (d) contacting at least some of the steam condensate withair; (e) deaerating at least some of the steam condensate which has beencontacted with air so that the concentration of oxygen therein is nogreater than about 50 PPBW; (f) using at least some of the deaeratedcondensate for scrubbing the steam produced from the geothermal brine;(g) separating flashed brine which has become contaminated with air fromflashed brine which has not been contaminated with air; (h) injectingthe flashed brine which has not become contaminated with air into theground through one or more injection wells; and (i) injecting theflashed brine which has been contaminated with air into the groundthrough one or more corrosion-protected injection wells.